* [Ada] Semantics of Delete for fixed strings
@ 2019-07-08 8:19 Pierre-Marie de Rodat
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From: Pierre-Marie de Rodat @ 2019-07-08 8:19 UTC (permalink / raw)
To: gcc-patches; +Cc: Ed Schonberg
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This patch corrects a bug in the implementation of Delete in an unusual
boundary case: the RM describes the semantics of Delete as equivalent to
that of Replace_String with a null argument. As a result, deleting a
null string that starts past the end of its argument is a noop and must
not raise Index_Error.
Tested on x86_64-pc-linux-gnu, committed on trunk
2019-07-08 Ed Schonberg <schonberg@adacore.com>
gcc/ada/
* libgnat/a-strfix.adb (Delete): The RM describes the semantics
of Delete as equivalent to that of Replace_String with a null
argument. As a result, deleting a null string that starts past
the end of its argument is a noop and must not raise
Index_Error.
gcc/testsuite/
* gnat.dg/fixed_delete.adb: New testcase.
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--- gcc/ada/libgnat/a-strfix.adb
+++ gcc/ada/libgnat/a-strfix.adb
@@ -192,7 +192,15 @@ package body Ada.Strings.Fixed is
elsif From not in Source'Range
or else Through > Source'Last
then
- raise Index_Error;
+ -- In most cases this raises an exception, but the case of deleting
+ -- a null string at the end of the current one is a special-case, and
+ -- reflects the equivalence with Replace_String (RM A.4.3 (86/3)).
+
+ if From = Source'Last + 1 and then From = Through then
+ return Source;
+ else
+ raise Index_Error;
+ end if;
else
declare
--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/fixed_delete.adb
@@ -0,0 +1,17 @@
+-- { dg-do run }
+
+with Ada.Text_IO; use Ada.Text_IO;
+with Ada.Strings.Fixed; use Ada.Strings.Fixed;
+
+procedure Fixed_Delete is
+ Str : String := "a";
+ Str1 : String := Replace_Slice (Str, 2, 2, "");
+ Str2 : String := Delete (Str, 2, 2);
+begin
+ if Str1 /= "a" then
+ raise Program_Error;
+ end if;
+ if Str2 /= "a" then
+ raise Program_Error;
+ end if;
+end Fixed_Delete;
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